Rotary atomization head

ABSTRACT

A rotary atomizing head assembly of the present invention is capable of washing off paint deposits from outer peripheral surface of a bell cup in a reliable manner. A paint reservoir (15) which is provided on a bell cup (11) is communicated with the outer peripheral surface of the bell cup (11) through solvent passages (16), and an annular guide (17) is provided around the outer peripheral side of the bell cup (11). Therefore, at the time washing the rotary atomizing head assembly (10), a thinner which is spouted out from a nozzle (6) is introduced into a solvent diffusing chamber (18) which is formed between the bell cup (11) and a enlarged front portion (17B) of the annular guide (17), through the paint reservoir (15) and solvent passages (16). After being diffused around the entire circumference of the bell cup (11) within the solvent diffusing chamber (18), the thinner is allowed to flow along the outer peripheral surface (11H) toward releasing edge (11D) at the fore end of the bell cup (11), washing away paint deposits from the outer peripheral surface (11H) of the bell cup (11).

TECHNICAL FIELD

This invention relates to a rotary atomizing head assembly particularlysuitable for use on a-coating machine with color changing functions

Generally speaking, electrostatic coating machines with a rotaryatomizing head assembly are largely constituted by; a coating machinebody; a rotational shaft which is axially extended and rotatablysupported on the coating machine body; an air motor which is mounted onthe coating machine body for driving the rotational shaft; a rotaryatomizing head assembly which is mounted in a fore distal end portion ofthe rotational shaft and driven from the air motor for rotation on thefront side of the coating machine body; and a feed nozzle which isreceived in the rotational shaft with its fore end portion extended intothe rotary atomizing head assembly The feed nozzle which serves forspurting a paint or a thinner as a washing solvent into the rotaryatomizing head assembly, is connected to a color changing valve deviceand a thinner source through pipings.

The rotary atomizing head assembly is formed in a bell- or cup-likeshape, including; a bell cup providing a paint spreading surface forspreading a paint into a-thin filmy form and a paint receiving surfacein fore and rear portions of its inner peripheral surface, respectively;a hub member mounted on the inner peripheral side of the bell cupbetween the paint spreading surface and the paint receiving surface; apaint reservoir formed between the rear surface of the hub member andthe paint receiving surface of the bell cup for temporarily holding apaint or solvent which is supplied to the paint receiving surface from afeed nozzle provided on the coating machine body; and a plural number ofpaint outlet holes provided in the hub member, for letting the paint orsolvent in the paint reservoir flow out therethrough onto the paintspreading surface of the bell cup.

In a paint coating operation by a prior art electrostatic coatingmachine of this sort, compressed air is supplied to the air motor in thefirst place to put the rotational shaft and rotary atomizing headassembly in high speed rotation. Thereafter, a paint is spurted into therotary atomizing head assembly through the feed nozzle, whereupon thesupplied paint is spread into a thin filmy form on the paint formingsurface on the inner peripheral side of the bell cup and then releasedin the form of charged particles from at marginal edge of the rotaryatomizing head assembly. At this time, the charged paint particles,which are released from the rotary atomizing head assembly, are urged tofly toward and deposit on a coating object, by traveling along lines ofelectric force in electrostatic field which is formed between theelectrostatic coating machine and the coating object.

During a paint coating operation by an electrostatic coating machine asdescribed above, paint inevitably deposits on the paint spreadingsurface as well as on the paint receiving surface of the bell cup. Inorder to wash paint deposits off the paint spreading surface, it is theusual practice to spurt a thinner onto the bell cup through a feednozzle while keeping the rotational shaft and the rotary atomizing headassembly in rotation by the air motor. Consequently, the thinner isspread over inner peripheral surface of the bell cup and urged to flowtoward the paint releasing edge through the paint spreading surface,washing away paint deposits therefrom

With a prior art electrostatic coating machine of this type, paintparticles which are released from the paint releasing edge at the foreend of a bell cup are mostly put on a flight toward a coating objectalong lines of electric force to deposit on the coating object However,it is often the case that part of released paint particles tend to flowin a reverse direction toward the outer peripheral side of the bell cupand deposit on outer peripheral surface of the bell cup.

Namely, when the rotary atomizing head assembly is put in high speedrotation, it is known in the art that inverse air flows are induced bythe air-pumping phenomenon, in which air is sucked into a negativepressure region which occurs on the front side of the bell cup under theinfluence of the high speed rotation of the rotary atomizing headassembly. As a consequence, part of released paint particles areentrained on inverse air flows toward rear side of the bell cup. Inaddition, in some cases shaping air is spurted out from the rotaryatomizing head assembly to shape the spray of paint particles into adesired pattern. In such a case, negative pressure regions are alsodeveloped partly around the outer peripheral side of the bell cup underthe influence of the jets of shaping air, also causing part of releasedpaint particles to flow in an inverse direction or toward the rear sideof the bell cup.

In case paint particles are partly entrained on inverse air flows inthis manner, the paint particles deposit on outer peripheral surface ofthe bell cup and remain there in a solidified state. Therefore, undercertain conditions of coating operation, solidified paint falls off insmall fragments which can detrimentally impair the quality of endproducts by depositing on coated surface. Further, according to theprior art electrostatic coating machine, the paint receiving andspreading surfaces of the bell cup are washed with a thinner which isspurted out toward the inner peripheral side of the bell cup from theafore-mentioned feed nozzle. However, difficulties are often experiencedin removing paint deposits from the outer peripheral surface of the bellcup simply by supplying a thinner through a feed nozzle in such amanner.

In this connection, in an attempt to solve the problem just mentioned,Japanese Utility Model Laid-Open No. S57-62659 (hereinafter referred toas "other prior art" for brevity) discloses an electrostatic coatingmachine employing a feed nozzle which is arranged to spurt a thinnertoward the outer peripheral surface of a bell cup. According to otherprior art electrostatic coating machine, while a rotary atomizing headassembly is being kept in rotation, a thinner is spurted onto the outerperipheral surface of the bell cup from a feed nozzle which is providedon a coating machine body, thereby washing away and removing depositedpaint therefrom

Nevertheless, according to the above-mentioned other prior art, athinner is simply spurted toward the outer peripheral surface of thebell cup just for washing the outer peripheral side of the rotaryatomizing head assembly, which is kept in rotation. Therefore, thethinner mostly is instantly shaken off the outer peripheral surfacewithout contacting the surface of the bell cup in a sufficient degree inaffinity or intimacy which is necessary for washing away paint depositsin a reliable manner.

In order to wash away paint deposits from outer peripheral surface ofthe bell cup in a more reliable manner, free of the above-mentionedproblems of the thinner being splashed around without contacting outerperipheral surface of the bell cup in a sufficient degree, it isnecessary to determine the position and direction of a wash feed nozzleprecisely and elaborately in relation with a thinner feed rate throughengineering processes which require extremely sophisticated machinedesigning and production technology.

Further, in view of complication in construction and increases in thenumber of machine parts and production cost, it is inefficient anduneconomical to provide a wash feed nozzle exclusively for the purposeof washing outer peripheral surface of a bell cup in addition to a feednozzle which is fitted in a rotational shaft of the rotary atomizinghead assembly for spurting a thinner toward inner peripheral surface ofthe bell cup as in the above-described prior art electrostatic coatingmachine.

DISCLOSURE OF THE INVENTION

With the above-mentioned problems of the prior art in view, it is anobject of the present invention to provide a rotary atomizing headassembly which can wash away paint deposits from outer peripheralsurface of a bell cup efficiently in a reliable manner.

In accordance with the present invention, as a solution to the problemsof the prior art as described above, there is provided a rotaryatomizing head assembly which basically includes; a bell cup formed in abell- or cup-shape, and having a paint spreading surface in a frontportion of its inner peripheral surface thereof for spreading a paintinto a thin filmy form and a paint receiving surface in a rear portionof the inner peripheral surface; a hub member mounted on the innerperipheral side of the bell cup between the paint spreading surface andthe paint receiving surface; a paint reservoir formed between a rearsurface of the hub member and the paint receiving surface of the bellcup for holding a supply of paint or solvent received from a nozzleprovided on a coating machine body; and a plural number of paint outletholes provided in the hub member, for letting the paint or solvent flowout from the paint reservoir onto the paint spreading surface on theinner peripheral side of the bell cup.

The rotary atomizing head assembly according to the present invention ischaracterized by the provision of; a plural number of solvent passageshaving respective entrance and exit openings located on the inner andouter peripheral surfaces of the bell cup, respectively, to communicatethe paint reservoir with the outer peripheral side of the bell cup; anannular guide mounted around the bell cup in spaced relation with theouter peripheral side of said bell cup to guide effluent solvent fromthe exit openings of the solvent passages; and a solvent diffusingchamber formed between and around the inner peripheral surface of theannular guide and outer peripheral surface of the bell cup to diffusethe solvent supplied thereto through the solvent passages.

With the arrangements just described, at the time of a coatingoperation, a paint is supplied to the paint reservoir through theabove-mentioned nozzle while rotating the rotary atomizing head assemblyat a predetermined speed. Consequently, under the influence ofcentrifugal force, the paint supplied to the paint reservoir is diffusedwithin the paint reservoir and urged to flow out to the paint spreadingsurface on the bell cup through the paint outlet holes which areprovided in the hub member. After being spread into a thin filmy form,the paint is released in the form of atomized particles at the fore endof the bell cup. Then, under the influence of electrostatic force,released paint particles are urged to fly toward and deposit on acoating object. In such a coating operation, the paint, which has ahigher viscosity as compared with solvent, is entirely led into thepaint outlet holes without entering the solvent passages.

For changing the paint color upon finishing a coating operation with acertain color, it is necessary to wash the rotary atomizing headassembly to remove paint deposits of previous color. In order to carryout a washing operation for this purpose, a solvent is spurted into thepaint reservoir from a solvent feed nozzle while holding the rotaryatomizing head assembly in rotation By so doing, the solvent is diffusedwithin the paint reservoir under the influence of centrifugal force, andpart of the solvent in the paint reservoir is urged to flow out throughthe paint outlet holes to the paint spreading surface and released fromreleasing edge at the fore end of the bell cup, thereby washing andcarrying away paint deposits of previous color from the paint spreadingsurface.

On the other hand, due to low viscosity, the residue of the solventwhich has been diffused within the paint reservoir is introduced intothe entrance openings of the solvent passages which lead to the outerperipheral side of the bell cup. Effluent solvent, which flows out ofthe exit openings of the solvent passages, is spread over and around theentire outer peripheral surface of the bell cup within the solventdiffusing chamber. Further, the solvent within the solvent diffusingchamber is guided toward the fore end of the bell cup by the annularguide and at the same time spattered on outer peripheral surface in afront portion of the bell cup. As a result, paint deposits of previouscolor on the outer peripheral surface in a front portion of the bell cupare washed away with the solvent.

According to one preferred form of the present invention, an annularridge or protuberance is provided in the solvent diffusing chamberbetween inner peripheral surface of the annular guide and outerperipheral surface of the bell cup for the purpose of dispersing flow ofthe solvent over and around the entire outer peripheral side of the bellcup within the solvent diffusing chamber.

With the arrangements just described, at the time of washing the rotaryatomizing head assembly, a solvent is spurted into the paint reservoirfrom a nozzle, and then introduced into the solvent diffusing chamberthrough the respective solvent passages. The solvent which flows throughthe solvent diffusing chamber is temporarily stopped by the annularprotuberance and dispersed over and around the entire solvent diffusingchamber. As a consequence, the solvent in the solvent diffusing chamberis dispersed over and around the entire outer peripheral side of thebell cup, and then allowed to flow out toward outer peripheral surfacein a front portion of the bell cup to wash away paint deposits fromentire outer peripheral surface of the bell cup.

In this instance, an annular protuberance may be provided on the innerperipheral surface of the annular guide and projected toward the outerperipheral surface of the bell cup to form an annular constrictedpassage between the annular guide and the bell cup.

With the arrangements just described, at the time of washing the rotaryatomizing head assembly, a solvent which is spurted into the paintreservoir through a solvent feed nozzle is introduced into the solventdiffusing chamber through the solvent passages. Then, the solvent isurged to flow toward the fore end of the bell cup under the guidance ofthe annular guide, and collided against the projecting annularprotuberance on the inner peripheral surface of the annular guide. As aresult, the solvent is dispersed over and around the entirecircumference of the bell cup within the solvent diffusing chamber. Inthis manner, the annular protuberance functions as a dam or weir fortemporarily stopping the forward flow of the solvent within the solventdiffusing chamber. After being dispersed over and around the entirecircumference of the bell cup, the solvent within the solvent diffusingchamber is then allowed to flow out through the annular constrictedpassage to outer peripheral surface of the bell cup on the front side ofthe annular protuberance to wash away paint deposits from the outerperipheral surface of the bell cup.

Alternatively, an annular protuberance may be provided on the outerperipheral surface of the bell cup in such a way as to project outwardlytoward the inner peripheral surface of the annular guide, therebyforming an annular constricted passage between the annular guide and thebell cup.

With the arrangements just described, the solvent which is introducedinto the solvent diffusing chamber at the time of atomizing headassembly washing operation can be similarly dispersed over and aroundthe entire circumference of the bell cup thanks to the dam effects ofthe annular protuberance. It follows that paint deposits on the outerperipheral surface of the bell cup can be washed away with the solvent.

According to another preferred form of the present invention, theentrance openings of the solvent passages are located in positionsinwardly spaced from the paint outlet holes by a predetermined distance.

With the arrangements just described, a paint which is spurted into thepaint reservoir through a nozzle during coating operation is urged toflow along rear surface of the hub member toward the paint outlet holes,without entering the solvent passages which are opened in positionsrearwardly spaced from the respective paint outlet holes. On the otherhand, at the time of atomizing head washing operation, a solvent whichis spurted into the paint reservoir through a nozzle is widely dispersedwithin the paint reservoir because of low viscosity as compared with thepaint, and urged to flow readily into the respective solvent passages.

According to the present invention, preferably the solvent passages areinclined in the rotational direction of the bell cup gradually fromentrance openings toward exit openings thereof.

With the arrangements just described, the solvent, which is introducedinto the paint reservoir through a nozzle at the time of atomizing headwashing operation, can be introduced into the solvent passages morereadily. Namely, since the bell cup is put in rotation in apredetermined direction during a rotary atomizing head assembly washingoperation, the solvent which has been introduced into the paintreservoir through a nozzle tends to swirl in the rotational direction ofthe bell cup. In this instance, the solvent can be urged to enter therespective solvent passages more readily since the inclination of thesolvent passages is related with the flow direction of the solventswirling in the paint reservoir.

Further, according to the present invention, the respective solventpassages are preferably inclined in a direction rearward of the bell cupgradually from the entrance openings toward the exit openings thereof.

With the arrangements just described, by inclination of the solventpassages toward the rear side of the bell cup, the respective solventpassages are extended in a direction different from centrifugaldirections (radial directions) of the bell cup. Therefore, even if apaint, which is fed to the paint reservoir through a paint nozzle, isdiffused in centrifugal directions during a coating operation under theinfluence of centrifugal force by high speed rotation of the bell cup,there is no possibility of the paint entering the solvent passages.

On the other hand, the solvent, which is lower than paint in viscosity,has properties of easily passing through narrow ducts. Therefore, at thetime of washing the rotary atomizing head assembly, the solvent, whichhas been supplied to the paint reservoir through a nozzle, can readilyflow into the respective solvent passages.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a longitudinal section of a rotary atomizing head assemblyaccording to a first embodiment of the present invention, showing therotary atomizing head assembly along with a rotational shaft and ashaping air ring;

FIG. 2 is a longitudinal section of the rotary atomizing head assemblyshown in FIG. 1;

FIG. 3 is a cross-section of the atomizing head assembly, taken in thedirection of arrows III--III in FIG. 2;

FIG. 4 is an enlarged longitudinal section through major components ofthe rotary atomizing head assembly of FIG. 1 in a washing operation;

FIG. 5 is a longitudinal section of a rotary atomizing head assemblyaccording to a second embodiment of the present invention;

FIG. 6 is a perspective view of the rotary atomizing head assembly ofthe second embodiment, having a shower of thinner on outer peripheralsurface of a bell cup for washing purposes;

FIG. 7 is a perspective view of the rotary atomizing head assembly ofthe first embodiment, having a shower of thinner on outer peripheralsurface of a bell cup similarly for washing purposes;

FIG. 8 is a longitudinal section through major components of a rotaryatomizing head assembly according to a third embodiment of the presentinvention;

FIG. 9 is a longitudinal section of a rotary atomizing head assemblyaccording to a fourth embodiment of the present invention;

FIG. 10 is a longitudinal section of a rotary atomizing head assemblyaccording to a fifth embodiment of the present invention;

FIG. 11 is a longitudinal section through major components of amodification of the rotary atomizing head assembly of the secondembodiment, having an annular protuberance provided in an axiallyintermediate portion of an annular guide; and

FIG. 12 is a longitudinal section through major components of amodification of the rotary atomizing head assembly of the thirdembodiment, having an annular protuberance provided on the part of abell cup in face to face relation with an axially intermediate portionof an annular guide

BEST MODE FOR CARRYING OUT THE INVENTION

Hereafter, the present invention is described more particularly by wayof its preferred embodiments with reference to the accompanyingdrawings.

Shown in FIGS. 1 through 4 is an electrostatic coating machine employinga rotary atomizing head assembly, which is according to a firstembodiment of the present invention.

In FIG. 1, indicated at 1 is a cover which forms the outer configurationof the electrostatic coating machine. Encased in the cover 1 are an airmotor 2, and a hollow rotational shaft 3 which is put in high speedrotation by the air motor 2.

Denoted at 4 is a feed tube which is passed through the rotational shaft3. This feed tube 4 is provided with a paint feed nozzle 5 and a solventfeed nozzle 6.

In this particular embodiment, the paint feed nozzle 5 has its base endconnected to a paint source through a paint valve or the like (both notshown in the drawings), and has its fore end protruded forward from thefore distal end of the rotational shaft 3 and extended into a rotaryatomizing head assembly 10 which will be described hereinafter. A paintis supplied to the rotary atomizing head assembly 10 through the paintfeed nozzle 5.

On the other hand, the solvent feed nozzle 6 is provided coaxiallyaround the paint feed nozzle 5. The solvent feed nozzle 6 has its rearend connected to a solvent source through a solvent valve or the like(both not shown in the drawings), and has its fore end located at thefore end of the rotational shaft 3 which is extended into the rotaryatomizing head assembly 10. A check valve 7 which is constituted by aresilient valve member or the like, is provided at the fore end of thesolvent feed nozzle 6. When the solvent valve is opened for washing therotary atomizing head assembly 10, a solvent or thinner is fed to thesolvent feed nozzle 6 under pressure, and introduced into the rotaryatomizing head assembly 10 as soon as the check valve 7 is opened by thepressure of the thinner.

Indicated at 8 is a shaping air ring which is provided at the fore endof the cover 1. The shaping air ring 8 is formed substantially in acylindrical shape, and provided with a plural number of shaping airoutlet holes 8A which are arranged annularly or circularly on its foreend face.

Designated at 9 is a shaping air supply passage, and this passage 9 isincluding an air passage 9A which is formed in the cover 1 and an airpassage 9B which is formed in the shaping air ring 8, and supplied withshaping air from an air source (not shown) to send the shaping airtoward the shaping air outlet holes 8A.

In this instance, shaping air is blown out through the shaping airoutlet holes 8A in the direction of arrow A to shape the spray ofreleased paint particles into a predetermined pattern. As will bedescribed hereinafter, shaping air also serves to restrict flowdirections of a thinner, which flows out through solvent passages 16 onthe bell cup 11, blowing the thinner against outer peripheral surface11H of the bell cup 11.

Indicated at 10 is the rotary atomizing head assembly which is mountedon the rotational shaft 3. As shown in FIG. 2, the bell cup 11, whichdefines the outer configuration of the rotary atomizing head assembly10, is formed in a bell- or cup-like shape enlarging the forwarddirection from a fitting base portion 11A to be mounted on a fore endportion of the rotational shaft 3 through threaded engagement therewith.Formed centrally of the bell cup 11 is a passage hole 11B of a smalldiameter for receiving therein the paint feed nozzle 5 and the checkvalve 7 of the solvent feed nozzle 6, which are protruded forward fromthe fore distal end of the rotational shaft 3.

Further, also on the inner peripheral side, the bell cup 11 is graduallyenlarged toward its front end from the passage hole 11B as the fashionof a skirt, providing a paint spreading surface 11C in a front portionfor spreading a supplied paint into a thin filmy form toward paintreleasing edge 11D which border the front end of the paint spreadingsurface lC. A paint receiving surface 11E for receiving either a paintor a thinner which is spouted out through the paint feed nozzle 5 orsolvent feed nozzle 6, is provided in a rear portion of the innerperipheral surface of the bell cup 11. Further, a hub mounting groove11F is formed between the paint spreading surface 11C and paintreceiving surface 11E for mounting a hub member 12 which will bedescribed hereinafter. Furthermore, a stepped mount portion 11G isformed in an axially intermediate portion on the outer peripheral sideof the bell cup 11.

Indicated at 12 is the hub member which is fitted in the hub mountinggroove 11F of the bell cup 11. The hub member 12 is formed in the shapeof a disk, and has its center axis located in alignment with the centeraxis of the rotary atomizing head assembly 10 (or with the axis of therotational shaft). Further, the hub member 12 is provided with a frontface 12A on its front side, which is formed in a flat shape continuouslyfrom the paint spreading surface 11C of the bell cup 11, and with apaint supply surface 12B on its rear side. The paint supply surface 12Bis provided with a conical projection 12C at the center thereof.

Denoted at 13 are a plural number of paint outlet holes which arearranged annularly or circularly along the outer peripheral side of thehub member 12. Through these paint outlet holes 13, a paint or asolvent, which has been spouted into the inner peripheral side of thebell cup 11 through the paint feed nozzle 5 or the solvent feed nozzle6, is allowed to flow out onto the paint spreading surface 11C.

Indicated at 14 are a plural number of solvent outlet holes which arebored at the foot of the conical projection 12C through from the paintsupply surface 12B to the front face 12A of the hub member 12. At thetime of washing the rotary atomizing head assembly 10, a thinner whichhas been spouted into the inner peripheral side of the bell cup 11 fromthe solvent supply nozzle 6 is allowed to flow out through these solventoutlet holes 14 to the front face 12A of the hub member 12.

Designated at 15 is a paint reservoir which is formed and definedbetween the paint supply surface 12B of the hub member 12 and the paintreceiving surface 11E of the bell cup 11 when the hub member 12 ismounted in position in engagement with the hub mounting groove 11F onthe bell cup 11. This paint reservoir 15 provides a space for spreadingand temporarily holding a certain amount of paint or solvent which hasbeen spouted into the bell cup 11 through the paint feed nozzle 5 orsolvent feed nozzle 6.

Indicated at 16 are a plural number of solvent passages, for example,twelve solvent passages which are formed at predetermined intervals inthe circumferential direction of the bell cup 11. Each one of thesolvent passages 16 is radially bored through the bell cup 11 to extendfrom the inner to the outer peripheral side thereof, with an entranceopening 16A opened on the paint receiving surface 11E and an exitopening 16B opened on the outer peripheral surface 11H of the bell cup11. At the time of washing the rotary atomizing head assembly 10, athinner which has been supplied to the paint reservoir 15 through thesolvent feed nozzle 6 is allowed to flow into these solvent passages 16and onto outer peripheral surface of the bell cup 11. Needless to say,there may be provided two to eleven or more than thirteen solventpassages 16 if desired.

In this particular embodiment, as shown in FIG. 4, the entrance openings16A of the respective solvent passages 16 are located inward of and at apredetermined distance a from the paint outlet holes 13. Namely, theentrance openings 16A of the solvent passages 16 are opened at positionswhich are spaced from the paint outlet holes 13 in a direction rearwardof the bell cup 11. Consequently, during a coating operation, a paintwhich is supplied to the paint reservoir 15 through the paint feednozzle 5 is prevented from flowing into the solvent passages 16. On theother hand, during a washing operation, a thinner which is supplied tothe paint reservoir 15 through the solvent feed nozzle 6 is allowed toflow into the solvent passages 16.

Further, from the entrance opening 16A toward the exit opening 16B, eachsolvent passages 16 is gradually inclined toward the rear side of thebell cup 11. Namely, the exit openings 16B of the solvent passages 16are located axially rearward of the respective entrance openings 16A forpreventing paint from flowing into the solvent passages 16 duringcoating operations.

Besides, as shown in FIG. 3, each solvent passage 16 is twisted in therotational direction of the rotary atomizing head assembly 10 (in thedirection of arrow B), gradually from the entrance opening 16A towardthe exit opening 16B. Namely, the respective solvent passages 16 aretwisted about the axis of the bell cup 11 through an angle α of from 15°to 50°. This arrangement makes it easier for the thinner to flow intothe respective solvent passages 16 after being spouted into the paintreservoir 15 through the solvent feed nozzle 6 during washing operationon the rotary atomizing head assembly 10.

Indicated at 17 is an annular guide which is fitted on the stepped mountportion 11G in a rear portion of the bell cup 11. The annular guide 17includes a fitting base portion 17A and a spreading or enlarged frontportion 17B which spreads in the shape of a bell or cup. In thisinstance, the annular guide 17 has the base portion 17A securely fixedon the stepped mount portion 11G of the bell cup 11, with the enlargedfront portion 17B extended toward the front side of the bell cup 11 in apredetermined spaced relation with outer peripheral surface 11H of thebell cup 11. Namely, the annular guide 17 is located to circumvent theouter peripheral side of the bell cup 11 in a spaced relation with thelatter.

Denoted at 18 is a solvent diffusing chamber which is formed between theinner peripheral surface of the enlarged front portion 17B of theannular guide 17 and the outer peripheral surface 11H of the bell cup11. This solvent diffusing chamber 18 is formed around the entirecircumference of the bell cup 11, and the exit openings 16B of theabove-described solvent passages 16 are opened into deep bottom portionsof this solvent diffusing chamber 18. In a washing operation on therotary atomizing head assembly 10, a thinner is urged to flow into thesolvent passages 16 from the paint reservoir 15 and then into thesolvent diffusing chamber 18 through the exit openings 16B of therespective solvent passages 16. Upon flowing into the solvent diffusingchamber 18, the thinner is diffused in circumferential directions.

With the arrangements as described above, the rotary atomizing headassembly 10 of the present embodiment can provide the followingfunctions and performances in paint coating operations.

At the start of a paint coating operation, the rotational shaft 3 isdriven from the air motor 2 for rotating the rotary atomizing headassembly 10 at a high speed in the direction of arrow B in FIG. 3, and apaint is introduced into the paint reservoir 15 on the rotary atomizinghead assembly 10 through the paint feed nozzle 5. As a result, the paintwhich has been fed to the paint reservoir 15 is urged to flow out to thepaint spreading surface 11C of the bell cup 11 through the respectivepaint outlet holes 13 and spread into a thin filmy form on the paintspreading surface 11C. At the paint releasing edge 11D, the thin film ofpaint is thrown forward in the form of liquid threads from the paintreleasing edge 11D, and atomized into fine particles.

At this time, since a high voltage is applied across the rotaryatomizing head assembly 10 and a coating object, the atomized andcharged paint particles, which are released from the rotary atomizinghead assembly 10, are urged to fly toward and deposit on a work to becoated. At this time, the spray of paint particles is shaped into apredetermined pattern by shaping air which is spurted out through therespective shaping air outlet holes 8A of the shaping air ring 8.

Paint deposits of a previously used color can be removed from the rotaryatomizing head assembly 10 by a washing operation as follows. Forwashing the rotary atomizing head assembly 10, a thinner is suppliedthrough the solvent feed nozzle 6 to the rotary atomizing head assembly10, which is put in rotation by the air motor 2 along with therotational shaft 3. Whereupon, the check valve 7 is opened as shown inFIG. 4, and the thinner is introduced into the paint reservoir 15through the solvent feed nozzle 6. In the paint reservoir 15, thethinner is diffused and urged to flow into the respective paint outletholes 13, solvent outlet holes 14 and solvent passages 16 as indicatedby arrow in FIG. 4.

In this instance, the thinner which has come out to the front side ofthe bell cup 11 through the paint outlet holes 13 is spread to flow overand along the entire paint spreading surface 11C of the bell cup 11, sothat paint deposits of previously used color are washed away from thepaint spreading surface 11C along with the thinner which is eventuallyreleased at the paint releasing edge 11D.

On the other hand, the thinner flowing out from the solvent outlet holes14 is spread and dispersed over the front face 12A of the hub member 12to wash away paint deposits of previously used color therewith, and thethinner is released from the paint releasing edge 11D of the bell cup 11after flowing across the paint spreading surface 11C.

Further, the thinner which has entered the solvent passages 16 isdirected in radially outward directions on leaving the exit openings 16Bof the each solvent passages 16, and then hit against the enlarged frontportion 17B of the annular guide 17 and temporarily pooled in thesolvent diffusing chamber 18. At this time, the thinner is diffusedaround the entire circumference of the bell cup 11.

The thinner within the solvent diffusing chamber 18 is then guidedtoward front portions of the bell cup 11 along the enlarged frontportion 17B of the annular guide 17, and allowed to flow toward the foreend of the bell cup 11 from the solvent diffusing chamber 18 to washaway paint deposits of previous color on the outer peripheral surface11H of the bell cup 11.

Thus, according to this embodiment, for washing the rotary atomizinghead assembly 10, a thinner is supplied to the paint reservoir 15through the solvent supply nozzle 6, and allowed to flow into thesolvent diffusing chamber 18 through the respective solvent passages 16,and this thinner is then guided toward front portions of the bell cup 11by the annular guide 17 and showered on the outer peripheral surface 11Hof the bell cup 11 to wash away paint deposits therefrom

Further, according to the present embodiment, as shown particularly inFIG. 4, the entrance openings 16A of the respective solvent passages 16are opened in deeper positions than the paint outlet holes 13, at adistance a from the latter. Therefore, the thinner is urged to flow intothe solvent passages 16 during a washing operation, and paint isprevented from flowing into the solvent passages 16 during a coatingoperation.

Namely, during a coating operation, major part of paint which has beenintroduced into the paint reservoir 15 flows on and along the paintsupply surface 12B of the hub member 12 toward the respective paintoutlet holes 13, so that there is little possibility of the paintflowing into the solvent passages 16 which are located in deeperpositions than the paint outlet holes 13. Besides, although part of thepaint in the paint reservoir 15 is diffused toward the paint receivingsurface 11E of the bell cup 11, the paint would not enter the entranceopenings 16A of the solvent passages 16 because of its higher viscosityand surface tension as compared with the solvent. In addition, therespective solvent passages 16 which are inclined toward the rear sideof the bell cup 11 functions to prevent inflow of the paint.

Further, according to the present embodiment, the provision of theannular guide 17 is arranged to circumvent the outer peripheral side ofthe bell cup 11, so that, at the time of a washing operation forremoving paint deposits of previous color from the rotary atomizing headassembly 10, the thinner which is scattered away from the exit opening16B of each solvent passage 16 under the influence of centrifugal forceis collided against inner peripheral surface of the enlarged frontportion 17B of the annular guide 17, thereby temporarily pooling in thesolvent diffusing chamber 18. As a result, all of the thinner whichcomes out through the respective solvent passages 16 is guided towardthe front side of the bell cup 11 by the annular guide 17 and showeredon the outer peripheral surface 11H of the bell cup 11.

Accordingly, when washing the outer peripheral surface 11H of the bellcup 11 with a thinner for removal of paint deposits therefrom, itbecomes possible to use the thinner very efficiently and economically,that is to say, to improve the washing efficiency to a marked degree byconsumption of the least amount of thinner.

Further, the thinner which has been introduced into the solventdiffusing chamber 18 through the respective solvent passages 16 isdiffused by the annular guide 17 along and over the outer peripheralsurface 11H of the bell cup 11 to wash away paint deposits from theentire outer peripheral surface 11H of the bell cup 11.

Moreover, according to the present embodiment having the respectivesolvent passages 16 inclined with a twist in the rotational direction ofthe rotary atomizing head assembly 10, a greater amount of thinner canbe sent into the solvent passages 16 in a reliable manner at the time ofwashing the rotary atomizing head assembly 10. Namely, as the rotaryatomizing head assembly 10 is rotated in the direction of arrow B, thethinner within the paint reservoir 15 is caused to flow in the samedirection as the rotary atomizing head assembly 10 (as indicated byarrow C) due to its viscosity. Consequently, in an assured manner, thethinner is urged to flow into the solvent passages 16 which are twistedin the direction of arrow B. Therefore, a large amount of thinner can beshowered on the outer peripheral surface 11H of the bell cup 11 throughthe solvent passages 16 and solvent diffusing chamber 18, washing awaypaint deposits on the outer peripheral surface 11H of the bell cup 11very effectively and reliably.

Furthermore, according to the present embodiment, the above-mentionedexcellent washing performance can be achieved simply by providing thesolvent passages 16 and annular guide 17 on the bell cup 11.Accordingly, in the case of an electrostatic coating machine of theso-called center feed tube type, it can be realized simply by addingsome changes to the rotary atomizing head assembly, withoutnecessitating reconstruction of the coating machine body proper. That isto say, a coating machine can be improved easily to enhance its washingperformance quality without entailing increases in cost or complicationsin construction.

Referring now to FIGS. 5 to 7, there is shown a rotary atomizing headassembly according to a second embodiment of the present invention. Thisembodiment has a feature in that an annular ridge or protuberance isprovided on the inner peripheral surface of the annular guide, theannular protuberance being projected toward the outer peripheral surfaceof the bell cup to form an annular constricted passage in cooperationwith the outer peripheral surface of the bell cup. In the followingdescription, except for the annular guide, the component parts which aresame as the corresponding parts in the foregoing first embodiment aresimply designated by common reference numerals or characters to avoidrepetition of same explanations.

In FIG. 5, indicated at 21 is a rotary atomizing head assembly accordingto this second embodiment, employing an annular guide 22 which issecurely fixed on a stepped mount portion 11G of the bell cup 11. Theannular guide 22 is substantially same as the annular guide 17 of thefirst embodiment, and provided with a fitting base portion 22A and aenlarged front portion 22B which is in the shape of a bell or cup. Theannular guide 22 is mounted on the bell cup 11 in such a way as tocircumvent the outer peripheral side of the bell cup 11 in spacedrelation with the bell cup 11. Therefore, a solvent diffusing chamber 23is defined between the inner peripheral surface of the enlarged frontportion 22B of the annular guide 22 and the outer peripheral surface 11Hof the bell cup 11.

Indicated at 24 is an annular protuberance which is provided on theinner peripheral surface of the enlarged front portion 22B of theannular guide 22. This annular protuberance 24 is located at and alongthe fore end of the enlarged front portion 22B, and projected toward theouter peripheral surface 11H of the bell cup 11 from the innerperipheral surface of the enlarged front portion 22B. Further, theannular protuberance 24 is formed endlessly around the entire innerperipheral surface of the annular guide 22, forming an annularconstricted passage 25 in cooperation with the outer peripheral surface11H of the bell cup 11.

In this instance, at the time of washing the rotary atomizing headassembly 21, the annular protuberance 24 at the fore end of the enlargedfront portion 22B of the annular guide 22 functions as a dam or weir fortemporarily stopping the flow of the thinner, which has been supplied tothe solvent diffusing chamber 23 through the exit openings 16B of therespective solvent passages 16 for circulation toward the fore end ofthe bell cup 11.

Having the construction just described, the rotary atomizing headassembly 21 of this embodiment operates basically in the same manner asthe foregoing first embodiment at the time of a washing operation

In the case of the rotary atomizing head assembly 21 of this embodiment,when it becomes necessary to wash off paint deposits of previous coloron the rotary atomizing head assembly 21 at the time of changing thepaint color, the rotary atomizing head assembly 21 is put in rotation bythe air motor 2 while supplying thinner to the paint reservoir 15through the solvent feed nozzle 6. The thinner which has been introducedinto the paint reservoir 15 is allowed to flow into the respective paintoutlet holes 13, solvent outlet holes 14 and solvent passages 16. Thus,paint deposits of previous color on the paint spreading surface 11C ofthe bell cup 11 are washed away with the thinner which flows out throughthe respective paint outlet holes 13, while paint deposits of previouscolor on the front face 12A of the hub member 12 are washed away withthe thinner which flows out through the respective solvent outlet holes14.

On the other hand, the thinner which has been passed through the solventpassages 16 is introduced into the paint diffusing chamber 23 from theexit openings 16B of the respective solvent passages 16. This portion ofthe thinner from the paint diffusing chamber 23 is urged to flow towardthe fore end of the annular guide 22 under the guidance of the annularguide 22 and then comes into collision against the annular protuberance24. As a result, the thinner is temporarily curbed by the weir effect ofthe annular protuberance 24 and spread over the entire circumference ofthe bell cup 11 in the paint diffusing chamber 23.

Then, after running over the annular protuberance 24 and flowing throughthe annular constricted passage 25, this part of the thinner is showeredon the outer peripheral surface 11H of the bell cup 11. As aconsequence, paint deposits on the outer peripheral surface 11H of thebell cup 11 can be completely washed away with the thinner from aroundthe entire circumference of the latter.

FIG. 6 shows the rotary atomizing head assembly 21 of the presentembodiment, in a perspective view taken obliquely from behind and above,the rotary atomizing head assembly 21 being in a phase of a washingoperation in which a thinner is spurted out from the solvent feed nozzle6 for two seconds. As seen in FIG. 6, paint deposits on the outerperipheral surface 11H of the bell cup 11 are completely washed away,without leaving any trace of paint deposits on the outer peripheralsurface 11H. This is because, thanks to the dam or weir effects of theannular protuberance 24 on the annular guide 22, the thinner is spreadover the outer peripheral surface 11H around the entire circumference ofthe bell cup 11 and, as indicated by arrows in FIG. 6, covering everypart of the entire circumference of the bell cup 11.

On the other hand, FIG. 7 shows the rotary atomizing head assembly 10 ofthe first embodiment similarly in a perspective view taken from behindand above, the rotary atomizing head assembly 10 being in a phase of awashing operation in which a thinner is spurted out from the solventfeed nozzle 6 for the same time period of two seconds, similarly to therotary atomizing head assembly 21 shown in FIG. 6. In this case, as seenin FIG. 7, part of paint deposits P (hatching parts) remains on theouter peripheral surface 11H of the bell cup 11. This occurs partlybecause of the absence of the annular protuberance on the annular guide17 of the rotary atomizing head assembly 10 of the first embodiment andpartly because of the thinner feed time of two seconds which is tooshort in this case to let the thinner spread over the entirecircumferential surface of the bell cup 11 to a sufficient degree. Evenin the case of the rotary atomizing head assembly 10 of the firstembodiment, however, it is possible to wash paint deposits off the bellcup 11 to a sufficient degree by prolonging the thinner feed time toabout five seconds, permitting the thinner within the solvent diffusingchamber 18 to spread over and around the entire circumference of thebell cup 11.

With the rotary atomizing head assembly 21 according to the presentembodiment as described above, the performance of the washing operationcan be enhanced all the more by providing the annular protuberance 24 onthe inner peripheral surface of the annular guide 22, for higherreliability of washing job, shorter washing time and reduced thinnerconsumption.

Illustrated in FIG. 8 is a rotary atomizing head assembly according to athird embodiment of the present invention. This embodiment is featuredby an annular protuberance or ridge which is provided on the outerperipheral surface of the bell cup and projected toward the innerperipheral surface of the annular guide, and by an annular constrictedpassage which is formed between the annular protuberance and the outerperipheral surface of the bell cup. In the following description of thethird embodiment, except for the bell cup, the component parts which aresame as the corresponding parts of the above-described first embodimentare simply designated by common reference numerals or characters toavoid repetition of same explanations.

Indicated at 31 is a rotary atomizing head assembly according to thepresent embodiment, and at 32 is a bell cup which defines the outerconfiguration of the rotary atomizing head assembly 31. The bell cup 32is formed in a bell- or cup-like shape, and largely constituted by afitting base portion 32A to be mounted on a rotational shaft, passagehole 32B, paint spreading surface 32C for distributing a paint in theform of a thin film, paint releasing edge 32D, paint receiving surface32E, hub mounting groove 32F, stepped mount portion 32G and outerperipheral surface 32H.

A hub member 12 is fitted in the hub mounting groove 32F of the bell cup32, defining a paint reservoir 33 between a paint receiving surface 12Bof the hub member 12 and the paint receiving surface 32E on the part ofthe bell cup 32.

Further, similarly to the above-described first embodiment, the bell cup32 is formed with a plural number of solvent passages 34 having therespective entrance and exit openings 34A and 34B opened on the paintreceiving surface 32E and the outer peripheral surface 32H of the of thebell cup 32, respectively. Further, an annular guide 17 is fitted on thestepped mount portion 32G of the bell cup 32, defining a solventdiffusing chamber 18 between the outer peripheral surface 32H of thebell cup 32 and the inner peripheral surface of the enlarged frontportion 17B of the annular guide 17.

The present embodiment is identical with the above-described firstembodiment in these aspects but differs from the bell cup 11 in that anannular protuberance 35 is provided on the part of the outer peripheralsurface 32H of the bell cup 32. More specifically, in the presentembodiment, an annular protuberance 35 is provided on the outerperipheral surface 32H of the bell cup 32 in such a position as toconfront fore end portions of the enlarged front portion 17G of theannular guide 17. The annular protuberance 35 is formed endlessly aroundthe entire circumference of the bell cup 32, and a constricted annularpassage 36 is formed between the annular protuberance 35 and theenlarged front portion 17B of the annular guide 17.

In this instance, the annular protuberance 35 at the fore end of theannular guide 17 similarly functions as a dam or weir for temporarilystopping the flow of thinner which is introduced into the solventdiffusing chamber 18 through the exit opening 34B of the respectivesolvent passages 34 for distribution toward the fore end of the bell cup32.

With the arrangements just described, the rotary atomizing head assembly31 of this embodiment can be washed in a reliable manner within ashortened time period and by the use of a smaller amount of thinner asin the foregoing first embodiment.

Referring now to FIG. 9, there is shown a rotary atomizing head assemblyaccording to a fourth embodiment of the present invention. Thisembodiment is featured by an annular guide which is formed integrallyaround the outer peripheral side of a bell cup. In the followingdescription of the fourth embodiment, the components such as hub member,paint outlet holes and solvent outlet holes, which are identical withthe counterparts in the foregoing first embodiment, are simplydesignated by similar reference numerals or characters to avoidrepetitions of same explanations.

Indicated at 41 is a rotary atomizing head assembly according to thepresent embodiment, and at 42 is a bell cup which defines the outerconfiguration of the rotary atomizing head assembly 41. In the samemanner as in the first embodiment, the bell cup 42 is formed in a bell-or cup-like shape, and constituted by fitting base portion 42A to bemounted on a rotational shaft, passage hole 42B, paint spreading surface42C for spreading a paint into a thin filmy form, paint releasing edge42D, paint receiving surface 42E, hub mounting groove 42F, and outerperipheral surface 42G. A hub member 12 is mounted in the hub mountinggroove 42F, defining a paint reservoir 43 between the paint supplysurface 12B of the hub member 12 and paint receiving surface 42E of thebell cup 42.

Denoted at 44 are a number of solvent passages, for example, twelvesolvent passages which are provided at predetermined intervals in thecircumferential direction of the bell cup 42. Similarly to the solventpassages 16 of the first embodiment, these solvent passages 44 similarlyhave the entrance openings 44A opened to the paint reservoir 43 and theexit openings 44B opened on the outer peripheral surface 42G of the bellcup 42.

Designated at 45 is an annular guide which is provided in an axiallyintermediate position on the outer peripheral side of the bell cup 42.This annular guide 45 is substantially in the same shape as theabove-described annular guide 17 of the first embodiment, except thatthe annular guide 45 is formed integrally with the bell cup 42. Asolvent diffusing chamber 46 is formed between the outer peripheralsurface 42G of the bell cup 42 and the inner peripheral surface of theannular guide 45.

With the arrangements just described, the rotary atomizing head assembly41 of the present embodiment can produce substantially the sameoperational effects as the foregoing first embodiment. Especially, itbecomes possible to reduce the number of parts in this case, by the useof the annular guide 45 which is formed integrally with the bell cup 42.

Referring now to FIG. 10, there is shown a rotary atomizing headassembly according to a fifth embodiment of the present invention. Thisembodiment is featured by a bell cup which is formed in an oblong oralmost cylindrical shape in its enlarged front portion and provided witha plural number of solvent passages along with an annular guide.

More specifically, indicated at 51 is a rotary atomizing head assemblyaccording to the present embodiment, and at 52 is a bell cup whichdefines the outer configuration of the rotary atomizing head assembly51. The bell cup 52 is formed in a bell- or cup-like shape, andincludes, similarly to the bell cup 11 of the above-described firstembodiment, fitting base portion 52A to be mounted on a rotationalshaft, passage hole 52B, paint spreading surface 52C for spreading apaint into a thin filmy form, paint releasing edge 52D, paint receivingsurface 52E, hub mounting groove 52F, stepped mount portion 52G, andouter peripheral surface 52H. In this case, however, the bell cup 52differs from the bell cup 11 of the first embodiment in that it isformed in an oblong shape in its enlarged front portion, presenting analmost cylindrical shape as a whole.

Denoted at 53 is a hub member which is fitted in the hub mounting groove52F of the bell cup 52 and which is constituted by a disc portion 53A ofcircular shape and a cylindrical anchor portion 53B. The disc portion53A is provided with a flat face 53C and a paint supply surface 53D onits front and rear sides, respectively.

Further, the hub member 53 is provided with a plural number of paintoutlet holes 54 which are arranged circularly in and along boundariesbetween its disc portion 53A and cylindrical portion 53B, along with aconical projection 53E which is formed centrally of the disc portion53A. A plural number of solvent outlet holes 55 are formed around footportions of the conical projection 53E.

Furthermore, the hub member 53 is fitted in the hub mounting groove 52Fof the bell cup 52 in such a way as to define a paint reservoir 56between its paint supply surface 53 and the paint receiving surface 52Eof the bell cup 52.

Indicated at 57 are a plural number of solvent passages, for example,twelve solvent passages which are provided at intervals in thecircumferential direction of the bell cup 52. These solvent passages 57have the respective entrance openings 57A opened on the paint receivingsurface 52E and the respective exit openings 57B opened on the outerperipheral surface 52H of the bell cup 52. Intermediate portions of thesolvent passages 57 are bored across the walls of the cylindricalportion 53B of the hub member 53. Namely, the cylindrical portion 53B ofthe hub member 53 is provided with intercommunicating bores 53F whichconstitute part of the solvent passages 57.

Denoted at 58 is an annular guide which is fitted on the stepped mountportion 52G of the bell cup 52. The annular guide 58 includes fittingbase portion 58A and a enlarged front portion 58B which extendsforwardly along the outer peripheral surface 52H of the bell cup 52,surrounding the bell cup 52 in spaced relation therewith. A solventdiffusing chamber 59 is formed between the outer peripheral surface 52Hof the bell cup 52 and the inner peripheral surface of the enlargedfront portion 58B of the annular guide 58.

With the arrangements just described, the rotary atomizing head assembly51 of the present embodiment can produce the same operational effects asin the foregoing first embodiment.

In the above-described second embodiment, the annular protuberance 24has been described as being provided at and along the fore end of theenlarged front portion 22B of the annular guide 22 as shown in FIG. 5.However, the present invention is not restricted to this particulararrangement, and includes other arrangements in which the annularprotuberance is located in an axially intermediate position or in a rearposition on the inner peripheral surface of the enlarged front portion22B of the annular guide 22. More specifically, as in a modificationshown in FIG. 11, an annular protuberance 24' may be provided in anaxially intermediate position on the annular guide 22.

Further, in the foregoing third embodiment of the present invention, theannular protuberance 35 has been described as being located in such aposition on the outer peripheral surface 32H of the bell cup 32 as toconfront face to face with a fore end portion of the enlarged frontportion 17B of the annular guide 17 as shown in FIG. 8. However, thepresent invention is not restricted to this particular arrangement, andincludes other arrangements in which the annular protuberance is locatedin an axially intermediate position or in a rear portion on the enlargedfront portion 17B of the annular guide 17. More specifically, as in amodification shown in FIG. 12, an annular protuberance 35' may beprovided in such a position as to confront an axially intermediateportion of the annular guide 17.

Furthermore, in the foregoing embodiments, the rotary atomizing headassembly according to the present invention has been described by way ofa center feed type electrostatic coating machine having the paint andsolvent feed nozzles 5 and 6 within the hollow rotational shaft 3.However, it is to be understood that the present invention can beapplied to other types of electrostatic coating machines adapted tospurt paint and thinner into a rotary atomizing head assembly from apaint feed pipe and a solvent feed pipe which are provided externally ofa rotational shaft.

Industrial Applicability

As clear from the foregoing particular description, the rotary atomizinghead assembly according to the present invention is provided with aplural number of solvent passages which communicate a paint reservoir ina bell cup with the outer peripheral side of the bell cup, along with anannular guide which is mounted in such a way as to surround the outerperipheral surface of the bell cup in spaced relation with the innerperipheral surface of the annular guide to define a solvent diffusingchamber therebetween. Therefore, a solvent, which is supplied to thepaint reservoir from a nozzle at the time of washing the rotaryatomizing head assembly, is introduced into the solvent diffusingchamber through the respective solvent passages and showered on theouter peripheral surface of the bell cup, thereby permitting to washaway paint deposits from the outer peripheral surface of the bell cup inan assured manner.

In addition, the solvent, which flows out to the outer peripheral sideof the bell cup through the respective solvent passages, is temporarilypooled in the solvent diffusing chamber and then allowed to flow towardthe fore end of the bell cup, thereby utilizing the entire amount ofeffluent solvent from the respective solvent passages effectively andeconomically in washing outer peripheral surface of the bell cup. Thus,the present invention makes it possible to use the solvent moreefficiently and to enhance the efficiency of washing operations to amarked degree

We claim:
 1. A rotary atomizing head assembly for paint coating machineincluding;a bell cup formed in a bell- or cup-shape, said bell cuphaving a paint spreading surface in a front portion of inner peripheralsurface thereof for spreading a paint into a thin filmy form and a paintreceiving surface in a rear portion of said inner peripheral surface; ahub member mounted on the inner peripheral side of said bell cup betweensaid paint spreading surface and said paint receiving surface; a paintreservoir formed between a rear surface of said hub member and saidpaint receiving surface of said bell cup for holding a supply of paintor solvent received from a nozzle provided on coating machine body; anda plural number of paint outlet holes provided in said hub member forletting said paint or solvent flow out from said paint reservoir to saidpaint spreading surface of said bell cup; characterized in that saidrotary atomizing head assembly comprises; a plural number of solventpassages having respective entrance and exit openings located on theinner and outer peripheral surfaces of said bell cup,-respectively, tocommunicate said paint reservoir with outer peripheral side of said bellcup; an annular guide mounted around said bell cup in spaced relationwith the outer peripheral side of said bell cup to guide effluentsolvent coming out of said exit openings of said solvent passages; and asolvent diffusing chamber formed between and around inner peripheralsurface of said annular guide and outer peripheral surface of said bellcup to diffuse said solvent supplied from said solvent passages.
 2. Arotary atomizing head assembly as defined in claim 1, further comprisingan annular protuberance provided in said solvent diffusing chamberbetween inner peripheral surface of said annular guide and outerperipheral surface of said bell cup for diffusing flow of said solventwithin said solvent diffusing chamber.
 3. A rotary atomizing headassembly as defined in claim 1, further comprising an annularprotuberance provided on inner peripheral surface of said annular guideand projected toward outer peripheral surface of said bell cup to forman annular constricted passage between said annular guide and said bellcup.
 4. A rotary atomizing head assembly as defined in claim 1, furthercomprising an annular protuberance provided on outer peripheral surfaceof said bell cup and projected toward inner peripheral surface of saidannular guide to form an annular constricted passage between saidannular guide and said bell cup.
 5. A rotary atomizing head assembly asdefined in claim 1, wherein said entrance openings of said solventpassages are located in positions inwardly spaced from said paint outletholes by a predetermined distance.
 6. A rotary atomizing head assemblyas defined in claim 1, wherein said solvent passages are inclined inrotational direction of said bell cup gradually from said entranceopenings toward said exit openings thereof.
 7. A rotary atomizing headassembly as defined in claim 1, wherein said solvent passages areinclined in a rearward direction of said bell cup gradually from saidentrance openings toward said exit openings.